Understand early animal evolution and phylogenetic relationships:
- Ediacaran fauna: Fossils from the Ediacaran period that represent some of the earliest multicellular life forms.
- Cambrian explosion: A significant event approximately 530 million years ago during which most major animal phyla appeared in the fossil record.
Characteristics of sponges:
- Morphology: Structural features of sponges.
- Gross & cell anatomy: Basic anatomical structure and cellular organization within sponges.
- Nutrition: How sponges obtain and process food.
- Similarity with choanoflagellates: Comparative aspects that show how sponges are related to this unicellular lineage.
Characteristics of cnidarians:
- Morphology: Structural characteristics of the cnidarian body plan.
- Nutrition: Feeding mechanisms of cnidarians.
Explain reasons for increase in bilaterian diversity and decrease in Ediacaran diversity during the Cambrian period:
- Factors and processes that led to diversification of bilaterians and the decline of Ediacaran fauna.
Unikonta
Classification:
- Includes „Protists”, which can be unicellular or multicellular organisms.
- Groups:
- Opistokonts: A supergroup of eukaryotes, including animals and fungi.
- Amoebozoans: Unicellular organisms that have a posterior flagellated ancestor, existing around 1000 million years ago (mya).
Animals: Traits
Basic characteristics:
- Heterotrophs: Organisms that ingest and digest food.
- Tubes: Reference to the digestive structure in many multicellular organisms.
- Multicellular: Composed of many cells.
- No cell walls: Unlike plant cells, animal cells do not have rigid cell walls.
- Collagen: A structural protein that is a primary component of the extracellular matrix in animal body tissues.
- Nerve and muscle cells: Specialized cells that facilitate movement and processing of information.
Example: Clam - a bivalve mollusc representing animal characteristics.
Animals: Traits 2
Reproduction:
- Diploid condition is dominant: Most animals are in the diploid stage for the majority of their life cycle.
- Sexual reproduction: Common method of reproduction among animals.
- Meiosis: A type of cell division that produces haploid gametes (sperm and eggs) from diploid cells.
- Sperm: Male gamete, small and flagellated.
- Egg: Female gamete, larger and nonmotile.
- Zygote: Formed by the fusion of sperm and egg during fertilization (syngamy), restoring diploid number.
History of Animals
Great diversity:
- Extinction: Over 99% of all animal species are extinct, highlighting the transient nature of biodiversity.
Ediacaran fauna: Early multicellular life forms that existed before the Cambrian explosion.
Cambrian fauna: Marked a period with a significant increase in animal diversity and complexity.
Evolution Timeline
Divergence timelines:
- Ancestors of fungi and animals: Diverged approximately 1,000 million years ago.
- Divergence of animals and choanoflagellates: Occurred between 761 to 957 million years ago.
DNA analyses: Reveal genetic connections between choanoflagellates and animals, providing insight into their common ancestry.
Fossil remains:
- Steroid fossils (~700 Mya): Evidence for the presence of ancient sponge (Porifera) relatives.
- Macroscopic fossils (~560 Mya): Larger, complex life forms from this time provide insight into early animal evolution.
Ediacaran Fossils
Dating: Ediacaran period spanned from 565 to 550 million years ago.
Indicators of early life: Included sponges and cnidarians, though some fossils do not match any living animals, indicating a unique evolutionary path.
Phylogeny of Animals
Classification of animals:
- Animals are monophyletic; they share a common ancestor.
- True tissues vs. no true tissues:
- Sponges (Porifera): Lack true tissues; represent basal animals.
- Cnidarians and others: Have true tissues; more derived in evolution.
- Diploblastic vs. Triploblastic:
- Diploblastic: Two primary germ layers – ectoderm and endoderm.
- Triploblastic: Three germ layers include mesoderm.
- Symmetry:
- Radial symmetry: Present in cnidarians and other simpler organisms.
- Bilateral symmetry: Characteristic of more complex animals e.g., bilaterians.
Porifera (Sponges)
Classification:
- Basal animals lacking true tissues.
- Characteristics:
- Monophyletic group; most are marine.
- Sedentary and act as suspension (filter) feeders.
Anatomy:
- Cell types: Key cell types include choanocytes and amoebocytes.
- Structure:
- Epidermis: Outer layer of cells.
- Pores: Small openings leading to the spongocoel (internal cavity).
- Choanocytes: Specialized cells within sponges used for feeding and water flow.
- Amoebocytes: Move through mesohyl, transporting nutrients and contributing to structural integrity.
Feeding:
- Water flow: Driven by the flagella of choanocytes, creating a flow of water through the sponge, facilitating filter feeding.
- Phagocytosis: Process by which food particles are engulfed and digested.
Regeneration in Sponges
Regenerative capabilities:
- Ability to replace lost or damaged body parts.
- Entire sponges can regenerate from a mass of cells as long as amoebocytes are present, reflecting a unique adaptation for survival.
Ctenophora (Comb Jellies)
Biological classification:
- Diploblastic organisms with true tissues from ectoderm and endoderm layers.
- Size: Range from a few millimeters to 1.5 meters; many are planktonic (drifting in water).
- Feeding behavior: Predatory, often using cilia for movement.
Cnidaria
Examples: Includes corals, jellies, and hydras.
- Classification: Diploblastic with two germ layers.
- Symmetry: Radially symmetrical body structure.
Morphology:
- Gastrovascular cavity: Functions as both mouth and anus, with a single opening.
- Polyp form: Attaches to a substrate (e.g., hydras, sea anemones).
- Medusa form: Free-moving, drifting by contracting body (e.g., jellyfish).
- Lifecycle: Some cnidarians exhibit both polyp and medusa forms in their life stages.
Nutrition in Cnidarians
Feeding mechanisms:
- Carnivorous; capture prey using tentacles.
- Process of digestion occurs in the gastrovascular cavity, where food is absorbed and undigested remnants expelled via the mouth/anus.
Historical Context and Cambrian Explosion
Divergence of major groups:
- Reiteration of earlier divergence events leading to modern animal phyla.
- Cambrian Explosion: Approximately 530 million years ago, marked the appearance of many modern animal phyla in the fossil record.
Cambrian Diversity:
- Fossils from this time include representatives of arthropods, chordates, and echinoderms.
- Development of hard, mineralized structures such as spines and body armor for protection.
- Evolution of bilaterians defined by their bilateral symmetry and complete digestive tracts.
Decline in Ediacaran Diversity
Reasons for decline during the Cambrian period:
- Predator/prey specialization: Evolution of both predators and prey drove diversification.
- Predator adaptations: Adaptations enhancing hunting capabilities.
- Development of mineralized structures: Increasing prevalence of calcium in the environment led to the development of protective features.
- Rising oxygen levels: Enhancement of metabolic rates facilitating larger body sizes.
- Hox genes: Emergence of developmental genes that determine body plans of bilaterally symmetrical animals, contributing to significant evolutionary innovation in body forms.